The HST team will be making a final decision on observing SDSS J153817.35+512338.0 based on the observations of May 13/14 and 14/15, and observations from the following two nights will also be essential. Close monitoring of 1RXS J105010.3-140431 through May 18 is requested. SDSS J153817.35+512338.0 is V=18.6 at minimum and its magnitude at maximum is unknown.

After SDSS J153817.35+512338.0, the next target will be the SU UMa-type dwarf nova DT Oct:

DT Oct 2013 May 23 23:31:07 through May 24 02:05:03 UT

This date is revised from the preliminary date given in AAVSO Special Notice #351. Giving SDSS J153817.35+512338.0 highest priority, please also monitor DT Oct; close monitoring May 17 through 25 is essential. DT Oct is V=16.5 at minimum and V=11.8 at maximum.

As instructed in AAVSO Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. For the magnitude estimates, a nightly V measurement from now through the HST observations and a day beyond would be best. If positive visual observations are possible, they are welcome, as are visual fainter-than observations fainter than magnitude 15.0.

Please report observations as soon as possible to the AAVSO International Database using the names SDSS J153817.35+512338.0 and DT Oct, respectively. If an outburst is detected, please report observations immediately. Many thanks!